PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior immunotherapy for SCLC and recovered No concurrent immunotherapy Chemotherapy: See Disease Characteristics At least 4 weeks since prior chemotherapy (6 weeks for carboplatin at doses of at least 500 mg/m2 or AUC more than 7 mg/mL) and recovered No more than 1 prior chemotherapy regimen No concurrent chemotherapy Endocrine therapy: At least 4 weeks since prior hormonal therapy for SCLC and recovered No concurrent steroids for brain metastasis No concurrent hormonal therapy Radiotherapy: See Disease Characteristics At least 2 weeks since prior radiotherapy and recovered No concurrent radiotherapy except palliative local radiotherapy for non-target lesions Surgery: At least 4 weeks since prior major surgery and recovered Other: At least 30 days since prior investigational drugs and recovered No other concurrent anti-cancer therapy No other concurrent investigational drugs